element (el´e-ment)

1. A substance composed of atoms of only one kind, i.e., of identical atomic (proton) number, that therefore cannot be decomposed into two or more e.'s, and that can lose its chemical properties only by union with some other e. or by a nuclear reaction changing the proton number. 2. An indivisible structure or entity. 3. A functional entity, frequently exogenous, within a bacterium, such as an extrachromosomal e. [L. elementum, a rudiment, beginning]
actinide e.'s actinides
alkaline earth e.'s those e.'s in the family Be, Mg, Ca, Sr, Ba, and Ra, the hydroxides of which are highly ionized and hence alkaline in water solution.
amphoteric e. an e. one or more of whose oxides unite with water to form hydroxides that may act as acids or as bases (e.g., aluminum).
anatomical e. any anatomical unit, such as a cell.morphologic e;
copia e.'s a mobile genetic e. with retrovirus-like sequence organization.
electronegative e. an e. whose atoms have a tendency to accept electrons and form negative ions (e.g., oxygen, sulfur, chlorine, etc.).
electropositive e. an e. whose atoms have a tendency to lose electrons and form positive ions (e.g., sodium).
extrachromosomal e. , extrachromosomal genetic e. plasmid
fold-back e.'s a type of transposable e. that possesses long inverted repeats, such that when denatured, loops are formed.
labile e.'s tissue cells, as of epithelium, connective tissue, etc., that continue to multiply by mitosis during the life of the individual.
long interspersed e.'s (LINES) long repetitive sequences in DNA with terminal repeats seen in human and mouse DNA.
morphologic e. anatomical e
neutral e. an e. of the zero group of the periodic system comprising the rare gases, He, Ne, Ar, Kr, Xe, Rn.noble e. (2);
noble e. 1. noble metal 2. neutral e
P e.'s a class of transposable e.'s in Drosophila responsible for hybrid dysgenesis; utilized as tools for introducing genes into new locations in the genome.
picture e. See pixel.
rare earth e.'s lanthanides
short interspersed e.'s (SINES) repetitive sequences of DNA of about 300 base pairs in length that occur about every 3000-5000 bp in the genome.
trace e.'s e.'s present in minute amounts in the body, many of which are essential in metabolism or for the manufacture of essential compounds; e.g., Zn, Se, V, Ni, Mg, Mn, etc..microelements, microminerals;
transposable e. a DNA sequence that can move from one location in the genome to another; the transposition event can involve both recombination and replication, producing two copies of the moving piece of DNA; the insertion of these DNA fragments can disrupt the integrity of the target gene, possibly causing activation of dormant genes, deletions, inversions, and a variety of chromosomal aberrations.
volume e. See voxel.


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